This protein oxidizes 4-hydroxyphenylpyruvate, a tyrosine and phenylalanine catabolite, to homogentisate. Homogentisate can undergo a further non-enzymatic oxidation and polymerization into brown pigments that protect some bacterial species from light. A similar process occurs spontaneously in blood and is hemolytic (see PMID:8000039). In some bacterial species, this enzyme has been studied as a hemolysin.